Acoustic noise reduction audio system having tap control

ABSTRACT

An acoustic noise reduction (ANR) headphone described herein has current detection circuitry that detects current consumed by an acoustic driver amplifier as a result of pressure changes due to a tapping of the headphone. Tapping may be performed to change an audio feature or operating mode of the audio system for the headphone. The current detection circuitry senses a characteristic of the current consumed by the acoustic driver amplifier that can be used to determine an occurrence of a tap event. Examples of a characteristic include an amplitude, waveform or duration of the sensed current. Advantageously, the ANR headphones avoid the need for control buttons to initiate the desired changes to the audio feature or operating mode.

BACKGROUND

This description relates generally to controlling the mode of an audiodevice and, more specifically, to acoustic noise reduction (ANR)headphones or headsets that can be controlled by the tap or touch of auser.

SUMMARY

In one aspect, an ANR audio system having tap control includes an ANRmodule, a current sensor, a signal conditioner module and an audio andmode control module. The ANR engine includes a first ANR engine input toreceive an audio input signal, a second ANR engine input to receive afirst supply current from a power supply through a first electricalpath, and an ANR engine output to provide an audio output signal. TheANR engine also includes an acoustic driver amplifier having a firstdriver amplifier input to receive a second supply current from the powersupply through a second electrical path, a second driver amplifier inputin communication with the ANR engine output to receive the audio outputsignal and a driver amplifier output to provide an amplified audiooutput signal. The current sensor is disposed in the second electricalpath and has a sensor output to provide a signal responsive to acharacteristic of the second supply current. The signal conditionermodule has an input in communication with the sensor output and has asignal conditioner output. The signal conditioner module provides aconditioned signal at the signal conditioner output in response to thesignal responsive to the characteristic of the second supply current.The audio and mode control module has a first input to receive a sourceaudio signal, a second input in communication with the signalconditioner output, and an output in communication with the first ANRengine input. The audio and mode control module controls at least one ofa mode of operation of a headphone system and an attribute of the audioinput signal in response to the conditioned signal.

Examples may include one or more of the following features:

The ANR audio system may further include an acoustic driver having adriver input in communication with the driver amplifier output of theacoustic driver amplifier to receive the amplified audio output signal.

The characteristic of the second supply current may include at least oneof an amplitude of the second supply current, a waveform representingthe second supply current and a duration of the second supply current.

The conditioned signal may be a logic level signal.

The current sensor may include an amplifier and a current sense resistorto receive the second supply current. The amplifier has a first input incommunication with an end of the current sense resistor, a second inputin communication with an opposite end of the current sense resistor, andan amplifier output to provide a voltage signal responsive to a voltageacross the current sense resistor. The signal conditioner module mayinclude at least one of a band-pass filter and a low-pass filter incommunication with the amplifier output of the current sensor. At leastone of the band-pass filter and the low-pass filter may have a maximumpass frequency of approximately 10 Hz.

The audio and mode control module may control at least one of aselection of an audio source, a volume, a balance, a mute, a pausefunction, a forward playback function, a reverse playback function, aplayback speed and a talk-through function.

In accordance with another aspect, a method for controlling an ANR audiosystem includes separating a supply current from a power supply into afirst current flowing to an ANR engine along a first electrical path anda second current flowing to an acoustic driver amplifier along a secondelectrical path. The second current flowing along the second electricalpath to the acoustic driver amplifier is sensed. A determination is madefrom the sensed second current that a tap event occurred. At least oneof a mode of operation of the audio system and an attribute of an audioinput signal is changed in response to the tap sequence of the tapevent.

Examples may include one or more of the following features:

The sensing of the second current may include sensing at least one of anamplitude of the second current, a waveform representing the secondcurrent and a duration of the second current.

The attribute of the audio input signal may include at least one of aselection of an audio source, a volume, a balance, a mute, a pausefunction, a forward playback function, a playback speed and a reverseplayback function.

In accordance with another aspect, a headphone includes a microphone, anANR module, a current sensor, a signal conditioner module and an audioand mode control module. The microphone detects a pressure change in acavity of the headphone, wherein the cavity includes an ear canal of awearer of the headphone. The ANR module includes an ANR engine having afirst ANR engine input to receive an audio input signal, a second ANRengine input to receive a first supply current from a power supplythrough a first electrical path, a third ANR engine input incommunication with the microphone, and an ANR engine output to providean audio output signal. The ANR module further includes an acousticdriver amplifier having a first driver amplifier input to receive asecond supply current from the power supply through a second electricalpath, a second driver amplifier input in communication with the ANRengine output to receive the audio output signal, and a driver amplifieroutput to provide an amplified audio output signal. The current sensoris disposed in the second electrical path and has a sensor output toprovide a signal responsive to a characteristic of the second supplycurrent. The signal conditioner module has an input in communicationwith the sensor output and has a signal conditioner output. The signalconditioner module provides a conditioned signal at the signalconditioner output in response to the signal responsive to thecharacteristic of the second supply current. The audio and mode controlmodule has a first input to receive a source audio signal, a secondinput in communication with the signal conditioner output, and an outputin communication with the first ANR engine input. The audio and modecontrol module controls at least one of a mode of operation of aheadphone system and an attribute of the audio input signal in responseto the conditioned signal.

Examples may include one or more of the following features:

The headphone may further include an acoustic driver having a driverinput in communication with the driver amplifier output of the acousticdriver amplifier to receive the amplified audio output signal.

The attribute of the audio input signal may include at least one of aselection of an audio source, a volume, a balance, a mute, a pausefunction, a forward playback function, a playback speed and a reverseplayback function.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of examples of the present inventiveconcepts may be better understood by referring to the followingdescription in conjunction with the accompanying drawings, in which likenumerals indicate like structural elements and features in variousfigures. The drawings are not necessarily to scale, emphasis insteadbeing placed upon illustrating the principles of features andimplementations.

FIG. 1 is a functional block diagram of an example of a circuit for anANR audio system having tap control.

FIG. 2 is a functional block diagram of an example of circuitry for anANR audio system having tap control.

FIG. 3 is a flowchart representation of an example of a method forcontrolling an ANR audio system having tap control.

FIG. 4 is a functional block diagram of a circuit that may be used toimplement one of the signal conditioner modules and the audio and modecontrol module of FIGS. 1 and 2.

FIG. 5 is a functional block diagram of another example of a circuit foran ANR audio system having tap control.

FIG. 6 is a flowchart representation of another example of a method forcontrolling an ANR audio system having tap control.

DETAILED DESCRIPTION

Various implementations described below allow a user to touch theoutside of a headphone or headset, or to touch the ear or nearby head asa means to instruct the performance of a desired function. As usedherein, an ANR headphone is any headphone or headset component that canbe worn in or about the ear to deliver acoustic audio signals to theuser or to protect the user's hearing, provides acoustic noise reductionor cancellation and has an exposed surface that can be tapped by a user.For example, an ANR headphone can be an ear cup that is worn on or overa user's ear, has a cushion portion that extends around the periphery ofthe opening to the ear as an acoustic seal, and a hard outer shell. ANRheadphones, as used herein, also include ANR earbuds that are typicallyat least partially inserted into the ear canal and have an exposedsurface that a user can tap or allow the user to tap the ear or a nearbyregion of the head.

Taps occurring in succession during a brief time period (e.g., severalseconds) are defined herein as a “tap event.” As used herein, a “tapsequence” refers to the content of the tap event, that is, the number ofindividual taps in the tap event. The tap sequence can be a single tapor can be two or more taps.

A tap event may be used to change a mode of operation of headphones orother components integrated with an ANR audio system. For example, thetap event can be used to change a headphone set from audio playback modeto a telephone communications mode. Alternatively, the tap event can beused to change a feature available in one mode that may not be availablein a different mode. Thus, the mapping of specific tap sequences toassociated functions is defined according to the particular mode ofoperation of the ANR audio system. The tap event is interpreted in lightof the current mode. For example, a tap sequence defined by a single tapduring playback may be interpreted as an instruction to pause thecurrent audio playback. In contrast, a single tap during telephonecommunications may be interpreted as an instruction to place a telephonecall on hold. Other examples include tapping a headphone one or moretimes to change the volume of an audio signal during playback, to skipto a subsequent audio recording in a playlist or sequence of recordings,to pause audio playback and to pair the headphones with another devicevia wireless communication, for example, using Bluetooth.Advantageously, the detection of the tapping of the external portion ofan ANR headphone, the ear or the head uses existing functionality withinthe ANR headphone. Moreover, the taps are reliably detected and can beused to control features available within a particular mode of operationof the headphones and to change to a different mode.

In an ANR headphone, noise is detected by a feedback microphone and ANRcircuitry generates a compensating signal to cancel that noise.Conventional ANR circuitry does not distinguish between the varioussources of pressure changes detected by the feedback microphone. Thepressure change can be acoustic noise or can be the result of a touchingof an exposed surface of the headphone, the external portion of the earor a region of the head near to the headphone to cause an acoustic orsubsonic pressure change. In response to the tap, the ANR circuitrygenerates a compensating signal.

In various examples, the visible portion of the ear made up of cartilageand skin, and which exists outside the head (i.e., the auricle orpinna), may be tapped to cause the pressure change in the sealed earcanal. Certain portions of the auricle, such as the helix, tragus, orantihelix, are more easily accessible to the user and can be tapped. Asused herein, a tap or headphone tap includes a direct touching of aheadphone or any intended touching of the ear or region of the head nearthe ear that causes a pressure change in the sealed ear canal. Tappingincludes tugging, “flicking” or pulling of skin and/or cartilage of theear or a portion of the head or skin on the head near the headphone. Asused herein, a sealed ear canal includes a substantially sealed earcanal in which a complete seal does not exist. For example, there may bea small gap between the headphone and the ear can through which air maypass and thereby reduce the amplitude of the pressure change for a tap;however, the pressure change may be sufficient for recognizing thepressure change as a tap.

Examples of ANR headphones and ANR systems described herein takeadvantage of a difference between general acoustic noise and taps to aheadphone based on a difference in the electrical current consumed bythe ANR circuitry. More specifically, a power supply current detectioncircuit is used to distinguish current consumed as a result of acousticnoise from current consumed by a tap event. A tap event results in highpressure within the headphone, and generally draws more current from thepower supply than that used to generate an acoustic noise cancellingsignal. When the current detection circuit senses a characteristic ofthe current, such as an amplitude and/or waveform or duration, thatcorresponds to an occurrence of a tap event, a signal indicative of thetap sequence for the tap event is provided to a microcontroller forinterpretation. For example, the microcontroller may be part of an audioand mode control module which initiates the changes to audio featuresand operating mode of the ANR system. The time occurring betweenconsecutive taps in a single tap sequence can be defined to be less thana predefined duration or a tap sequence can require that all taps occurwithin a predefined time interval, for example, several seconds.Advantageously, the ability to tap a headphone to cause a change in modeor audio signal attribute avoids the use of control buttons to implementsimilar functions. Control buttons are often problematic for a user,especially when the buttons are located on a portion of the system thatmay be located in a pocket or on the arm of a user, or are located on asmall or difficult to reach area of the headphone. For example, in thecontext of headsets used by pilots in aircraft, searching for buttonsthat are located on a peripheral or difficult to reach area may bedistracting from focusing on the surroundings and the pilot's primarytask.

FIG. 1 is a functional block diagram of an example of a circuit 10 foran ANR audio system having tap control. The circuit 10 includes an ANRmodule 12, a current sensor 14, a signal conditioner module 16, an audioand mode control module 18 and a power supply 20. The circuit 10 isconfigured to provide a signal to drive at least one acoustic driver(“speaker”) 22 in a headphone cavity 24 and to receive a microphonesignal from a microphone 26 in the headphone cavity 24. Although shownseparately, it will be appreciated in light of the description belowthat certain elements of the signal conditioner module 16 and audio andmode control module 18 may be shared elements.

The ANR module 12 includes a first input 28 that receives an audio inputsignal from the audio and mode control module 18 and a second input 30that receives a supply current I_(S) from the power supply 20. By way ofexample, the power supply can be one or more batteries, DC powerprovided by the audio source, or may be an electrical power convertersuch as a device that uses alternating current (AC) power and providesdirect current (DC) power at a desired voltage level. The ANR module 12includes an ANR output 32 that provides an audio output signal to thespeaker 22. In the illustrated circuit 10, the ANR module 12 alsoincludes various other components including an amplifier 50, feedbackcircuitry 52 and a summing node 54 as are known in the art. Althoughshown as using feedback compensation, the ANR module 12 canalternatively use feedforward correction or a combination of feedbackcorrection and feedforward correction based, at least in part, on amicrophone signal generated by the microphone 26 in response to receivedacoustic energy. In a feedforward implementation, an additionalmicrophone (not shown) may be used to detect noise external to theheadphone, and provide a signal cancelling that noise. When bothfeedforward and feedback correction are used, the feedback microphone 26detects the residual noise in the headphone cavity 24 after thefeedforward system has functioned to cancel noise detected external tothe headphone.

The current sensor 14 has a sensor input 34 to receive the supplycurrent Is from the power supply 20 and a sensor output 36 that providesa signal responsive to a characteristic (e.g., an amplitude and/orwaveform or duration) of the supply current I_(s). The signalconditioner module 16 includes an input 38 in communication with theoutput 36 of the current sensor 14 and an output 40 that provides aconditioned signal to the audio and mode control module 18. Theconditioned signal is a logic level signal (e.g., a low or high logicvalue digital pulse) generated according to the signal provided at thesensor output 36. As illustrated, the current sensor 14 includes a“sensing” resistor 56 and an amplifier 58 having differential inputs tosense a voltage across the resistor 56.

The audio and mode control module 18 includes an input 42 to receive asignal from an audio source 44, another input 46 to receive theconditioned signal and an output 48 in communication with the firstinput 28 of the ANR module 12. The audio source for the headphone may bedifferent than the audio source for a second headphone (not shown). Forexample, one audio source may provide a left channel audio signal andthe other audio source may provide a right channel audio signal. Theaudio and mode control module 18 is used to control a mode of operationof the ANR audio system, an attribute of the audio input signal, orboth, in response to the conditioned signal. Examples of modes include,but are not limited to, music playback, telephone mode, talk throughmode (e.g., temporary pass through of a detected voice), a level ofdesired ANR, and audio source selection. Examples of attributes of theaudio input signal include, but are not limited to, volume, balance,mute, pause, forward or reverse playback, playback speed, selection ofan audio source, and talk through mode.

During typical operation, the audio output signal from the ANR module 12is received at the speaker 22 and results in production of an acousticsignal that substantially reduces or eliminates acoustic noise withinthe headphone cavity 24. The audio output signal may also generate adesired acoustic signal (music or voice communications) within theheadphone cavity 24.

ANR headphones generally operate in a manner to independently reduceacoustic noise in each headphone. Thus, each ANR headphone includes allthe components shown in FIG. 1 except for the audio and mode controlmodule 18 and power supply 20 which may be “shared” with each headphone.FIG. 2 is a functional block diagram of an example of circuitry 60 thatincludes circuits for implementing ANR for a headphone system. Thecircuitry 60 includes two circuits that are similar to the circuit 10 ofFIG. 1. Reference numbers in the figure that are followed by an “A”indicate elements associated with a circuit for one headphone (e.g.,left headphone) and reference numbers followed by a “B” indicateelements associated with a circuit for the other headphone (e.g., rightheadphone). Reference numbers lacking an “A” or “B” are generallyassociated with shared circuit components, though in some examples, theymay be provided individually in each headphone.

Reference is also made to FIG. 3 which shows a flowchart representationof an example of a method 100 for controlling an ANR audio system havingtap control. During operation, the amplitude and/or waveform or durationof the supply current I_(S) to each headphone is sensed (step 110) bymonitoring the voltage drop across the sensing resistor 56. When an earcup (or earbud) is tapped by a user or when the ear or region of theuser's head near to the ear is tapped, the volume of the cavity definedby the ear cup and the user's ear canal changes due to the compliancesof the cushion and user's skin. The result is a change in the pressurewithin the ear cup and ear canal, which is sensed by the microphone 26.The ANR module 12 responds by sending an electrical signal to thespeaker 26 that produces an acoustic signal within the cavity intendedto eliminate the pressure change caused by the tap. The electricalsignal provided at the output 32 of the ANR module 12 is sourced fromthe amplifier 50 which in turn consumes the supply current I_(S) fromthe power supply 20. Thus, a tap applied by a user to the headphone canbe recognized as a significant variation in the amplitude and/orwaveform or duration of the supply current I_(S).

The user may simply tap the headphone, ear or head a single time or maymake multiple taps in rapid succession in order to change in a mode ofoperation of the ANR system or an attribute of the audio signal receivedfrom the audio sources 44. A determination is made (step 120) that asequence of taps, including a single tap or multiple taps, has occurred.The mode of operation of the ANR system or an attribute of the audioinput signal is changed (step 130) in response to the taps in thesequence. The steps of the method 100 are executed using the currentsensor 14, signal conditioner module 16 and audio and control module 18.As each headphone has a current sensor 14 and a signal conditioner 16,either headphone or its associated ear or head region can be tapped tochange the mode of operation or audio input signal attribute. Moreover,as described in more detail below, the simultaneous monitoring of thesupply current I_(s) for each headphone allows the determinationaccording to step 120 to include a discrimination between a valid usertap and a different event that might otherwise be erroneouslyinterpreted as a user tap. By way of example, a disturbance common toboth headphones, such as dropping a headphone set, disconnecting theheadphone set from an audio system or the occurrence of a loud “externalacoustic event”, may result in a determination that both headphones havebeen tapped by a user. If it appears that both headphones have beentapped at nearly the same time, the ANR audio system ignores thedisturbance and the mode and audio signal attributes remain unchanged.

Various circuit elements can be used to implement the modules present inthe circuitry 60 of FIG. 2. For example, FIG. 4 shows a functional blockdiagram of a circuit 70 that may be used to implement the signalconditioner module 16A for the left headphone (similar circuitry couldbe used for the right headphone) and the audio and mode control module18. Referring to FIG. 2 and FIG. 4, the circuit 70 includes a band-passfilter (BPF) 72, which filters the signal provided by the amplifier 58in the current sensor 14. In other examples, the filter may be alow-pass filter. By way of one non-limiting example, the band-passfilter 72 can have a minimum pass frequency of approximately 0.1 Hz and,in another example, the band-pass filter 72 (or low-pass filter) canhave a maximum pass frequency of approximately 10 Hz. A non-zero minimumpass frequency prevents a near-DC event, such as a slow pressureapplication in which a headphone is slowly pressed against an object,such as a chair, from being interpreted as a tap event. The filteredsignal is received at a first input 74 of a comparator 76 and areference voltage source 78 is coupled to a second input 80 of thecomparator 76. By way of example, the reference voltage source 78 can bea voltage divider resistive network coupled to a regulated power supply.A comparator output signal at the comparator output 82 is a logic value(e.g., HI) that indicates a possible tap event when the voltage at thefirst input 74 exceeds the “threshold voltage” applied to the secondinput 80 and otherwise is a complementary logic value (e.g., LO).

The comparator output signal, indicative of a possible tap event when ata logic HI value, is applied to a clock input 98 of a monostablevibrator 96. There can be occurrences when a signal of sufficientfrequency and amplitude can cause excessive current through the currentsensor 14 and therefore cause an affirmative signal at the comparatoroutput 82 yet not result from a valid tap to a headphone. For example, aloud noise near a user might be sufficient to cause the comparatoroutput signal to indicate a tap event. The circuit 70 provides furthercomponents to prevent invalid events from being interpreted as valid tapevents. The comparator output signal is also applied to an inputterminal 84 of an AND gate 86 and the comparator output signal from acounterpart comparator (e.g., right channel comparator, not shown) forthe other (e.g., right) headphone channel is provided to the other inputterminal 88. Thus, the AND gate 86, which is applied to an input 90 of aNOR gate 92, produces a logic value (e.g., HI) if the comparator outputsignals for both the left and right headphone channels are logic HI. Inturn, the NOR gage 92 inverts the logic HI signal to a logic LO signalthat is applied to the enable input 94 of the monostable vibrator 96,thereby disabling the comparator output signal applied to the clockinput 98 of the monostable vibrator 96 from appearing at the output 100.Thus, occurrences that would generate a change in pressure in both theleft and right headphones that could be mistaken for a tap event (e.g.,a loud noise near the user), are not interpreted as a tap event.

Another potential means for causing an erroneous determination of a tapevent is a power supply transient event such as a powering on orpowering off transient condition. A voltage detector 102 is incommunication with the power supply and provides a logic signal (e.g.,HI) at its output 104 indicating an excessive power supply voltage, thatis, that the applied voltage has transitioned from less than a thresholdvoltage to greater than a threshold voltage. Conversely, the logicsignal at the output 104 will change to a complementary logic value(e.g., LO) when the applied voltage transitions from greater than thethreshold voltage to less than the threshold voltage. A delay module 106receives the logic HI signal from the voltage detector 102 and holds thelogic value until the expiration of a set time period (e.g., 0.5 s,though other periods of time could be used). This signal is applied to asecond input 110 of the NOR gate 92 which in turn disables themonostable vibrator 96 to prevent a false indication of a tap event.

In addition, there can be unwanted transients in an audio channel of theheadphone. For example, if a headphone jack is plugged into an audiodevice or if there is an electrostatic discharge occurrence, there maybe a loud noise such as a “popping” or “crackling” due to an excessivepeak voltage in the audio signal which, if not properly processed, maybe sufficient to trigger a false indication of a tap event. An amplitudethreshold module 112 receives the left channel audio signal and providesa delayed output signal at the output terminal 114 with a valuecorresponding to peaks in the voltage level of the audio signal. Acomparator 116 receives the output signal from the delay module 112 at afirst input terminal 118 and a voltage from a reference voltage source126 is applied to a second input terminal 120. The reference voltage isselected to correspond to a voltage value above which the delayed outputsignal is considered to indicate an audio occurrence that is not a validtap event. Thus, if the signal at the first input terminal 118 exceedsthe signal at the second input terminal 120, a logic HI signal isgenerated at the comparator output 122 and applied to an input 124 ofthe NOR gate 92. As a result, the NOR gate 92 applies a logic LO signalto the enable input 94 of the monostable vibrator 96 to disable thecomparator output signal at the clock input 98 of the monostablevibrator 96 from appearing at the output 100.

In the detection of error conditions described above, the NOR gate 92 isa logic element that includes a number of inputs with each inputreceiving a logic signal indicative of a particular error condition. Theoutput of the logic element provides a logic signal having a first stateif at least one of the error conditions exists and a second state ifnone of the error conditions exist. The logic signal at the output isused to prevent a determination of a tap event for circumstancesunrelated to a tap event. Thus, the circuit 70 described above providesfor determining the states of various error conditions, that is,conditions that can lead to a determination of a tap event without auser actually tapping a headphone. The circuit 70 prevents suchconditions from causing a change in an audio attribute or operationalmode of ANR headphones or an ANR audio system.

In one alternative configuration, the comparator 76 is implementedinstead as a discriminator that uses two thresholds instead of a singlethreshold to determine a valid tap event. The two thresholds may beselected so that the filtered signal from the bandpass filter 72 isinterpreted to indicate a valid tap event if the voltage exceeds a lowerthreshold voltage and does not exceed the higher threshold voltage. Inthis way extreme amplitude events that “pass” the lower thresholdvoltage requirement, but are not initiated by a user tap, are preventedfrom being interpreted as valid tap event. By way of one example,removing a single headphone from the head of a user may result in such ahigh amplitude event.

Referring again to the examples of circuits for an ANR audio systemhaving tap control as shown in FIGS. 1 and 2 and described above, thesupply current I_(S) provided to the ANR module 12 is sensed todetermine the occurrence of a tap event. The current consumed by theamplifier 50 is typically insignificant compared to the current consumedby other components of the ANR module 12. These other components arecollectively referred to below as an ANR engine and the current consumedby the ANR engine is referred to as a quiescent current. Even during atap, the increased current consumed by the amplifier 50 is substantiallyless than the quiescent current which remains nearly constant regardlessof the magnitude of the audio input signal. Consequently, it can bedifficult to sense the change in the supply current Is due to a tapevent since the supply current is primarily consumed by the ANR engine.Stated alternatively, it can be difficult to sense a small current spikethat is present on a much greater constant quiescent current.

FIG. 5 is a functional block diagram of an example of a circuit 150 foran ANR audio system having tap control. The circuit 150 includescomponents similar to those depicted in FIG. 1, including an ANR module152 having an acoustic driver amplifier 154 and an ANR engine 156. TheANR engine 156 may include all the elements of the ANR module 152 otherthan the amplifier 154. For example, the ANR engine may include elementsof the feedback circuit 52 of FIG. 1 and/or components of a feedforwardcircuit.

The ANR engine 156 has a first ANR engine input 158 to receive an audioinput signal, a second ANR engine input 160 to receive a first supplycurrent I₁ conducted through a first electrical path 162 and an ANRengine output 164 to provide an audio output signal. The acoustic driver154 has a first driver amplifier input 166 to receive a second supplycurrent I₂ conducted through a second electrical path 168, a seconddriver input 170 in communication with the ANR engine output 164 toreceive the audio output signal, and a driver amplifier output 172 toprovide an amplified audio output signal.

A power supply 20, such as a battery, provides a supply current I_(S)which is separated into two separate currents at node 174. Morespecifically, the first supply current I₁ flows from the node 174 alongthe first electrical path 162 to the ANR engine 156 and the secondsupply current I₂ flows from the node 174 along the second electricalpath 168 through the current sensor 14 to the acoustic driver amplifier154.

In the illustrated circuit 150, the current sensor 14 senses only thesecond supply current I₂. Thus, the spike in the magnitude of the sensedcurrent is a substantially larger portion of the total current thoughthe current sensor 14 than for the circuit 10 of FIG. 1 as the secondsupply current I₂ is nearly zero other than during a tap event. As aresult, the detection of a tap event with the circuit 150 is generallymore robust.

Reference is also made to FIG. 6 which is a flowchart representation ofanother example of a method 200 for controlling an ANR audio systemhaving tap control. According to the method 200, the supply currentI_(S) from the power supply 20 is separated (step 210) into a firstcurrent I₁ flowing along the first electrical path 162 to the ANR engine156 and a second current I₂ flowing to the acoustic driver amplifier154. The second current I₂ is sensed (step 220) by the current sensor14. A determination is made (step 230) from the sensing of the secondcurrent I₂ that a tap event occurred. In response to determining the tapevent, a mode of operation of the audio system and/or an attribute of anattribute of the audio input signal is changed (step 240).

In other examples of circuits for an ANR audio system having tapcontrol, the current sensor 14 and/or signal conditioner 16 may beincluded as a component in the ANR module 152 as long as they aredisposed along the second electrical path 168. Moreover, the ANR engine156 may be on an integrated circuit (IC) chip and the acoustic driveramplifier may be a discrete element or a component on a second IC chip.The circuit 150 can be implemented as a modification to the circuitry 60of FIG. 2, that is, the circuit 150 can be used with a left headphoneand another circuit 150 used with a right headphone.

The circuitry of FIGS. 1, 2, 4 and 5 may be implemented with discreteelectronics, by software code running on a digital signal processor(DSP) or any other suitable processor within or in communication withthe headphone or headphones.

Examples of the systems and methods described above comprise computercomponents and computer-implemented steps that will be apparent to thoseskilled in the art. For example, it should be understood by one of skillin the art that the computer-implemented steps may be stored ascomputer-executable instructions on a computer-readable medium such as,for example, floppy disks, hard disks, optical disks, Flash ROMS,nonvolatile ROM, and RAM. Furthermore, it should be understood by one ofskill in the art that the computer-executable instructions may beexecuted on a variety of processors such as, for example,microprocessors, digital signal processors, gate arrays, etc. For easeof exposition, not every step or element of the systems and methodsdescribed above is described herein as part of a computer system, butthose skilled in the art will recognize that each step or element mayhave a corresponding computer system or software component. Suchcomputer system and/or software components are therefore enabled bydescribing their corresponding steps or elements (that is, theirfunctionality), and are within the scope of the disclosure.

A number of implementations have been described. Nevertheless, it willbe understood that the foregoing description is intended to illustrate,and not to limit, the scope of the inventive concepts which are definedby the scope of the claims. Other examples are within the scope of thefollowing claims.

What is claimed is:
 1. An acoustic noise reduction (ANR) audio systemhaving tap control, comprising: an ANR module comprising: an ANR enginecomprising a first ANR engine input to receive an audio input signal, asecond ANR engine input to receive a first supply current from a powersupply through a first electrical path, and an ANR engine output toprovide an audio output signal; and an acoustic driver amplifier havinga first driver amplifier input to receive a second supply current fromthe power supply through a second electrical path, a second driveramplifier input in communication with the ANR engine output to receivethe audio output signal and a driver amplifier output to provide anamplified audio output signal; a current sensor disposed in the secondelectrical path and having a sensor output to provide a signalresponsive to a characteristic of the second supply current; a signalconditioner module having an input in communication with the sensoroutput and having a signal conditioner output, the signal conditionermodule providing a conditioned signal at the signal conditioner outputin response to the signal responsive to the characteristic of the secondsupply current; and an audio and mode control module having a firstinput to receive a source audio signal, a second input in communicationwith the signal conditioner output, and an output in communication withthe first ANR engine input, the audio and mode control modulecontrolling at least one of a mode of operation of a headphone systemand an attribute of the audio input signal in response to theconditioned signal.
 2. The ANR audio system of claim 1 furthercomprising an acoustic driver having a driver input in communicationwith the driver amplifier output of the acoustic driver amplifier toreceive the amplified audio output signal.
 3. The ANR audio system ofclaim 1 wherein the characteristic of the second supply currentcomprises at least one of an amplitude of the second supply current, awaveform representing the second supply current and a duration of thesecond supply current.
 4. The ANR audio system of claim 1 wherein theconditioned signal is a logic level signal.
 5. The ANR audio system ofclaim 1 wherein the current sensor comprises: a current sense resistorto receive the second supply current; and an amplifier having a firstinput in communication with an end of the current sense resistor, asecond input in communication with an opposite end of the current senseresistor, and an amplifier output to provide a voltage signal responsiveto a voltage across the current sense resistor.
 6. The ANR audio systemof claim 1 wherein the audio and mode control module controls at leastone of a selection of an audio source, a volume, a balance, a mute, apause function, a forward playback function, a reverse playbackfunction, a playback speed and a talk-through function.
 7. The ANR audiosystem of claim 5 wherein the signal conditioner module comprises atleast one of a band-pass filter and a low-pass filter in communicationwith the amplifier output of the current sensor.
 8. The ANR audio systemof claim 7 wherein the at least one of a band-pass filter and a low-passfilter has a maximum pass frequency of approximately 10 Hz.
 9. Aheadphone comprising: a microphone for detecting a pressure change in acavity of the headphone, the cavity comprising an ear canal of a wearerof the headphone; an ANR module comprising: an ANR engine having a firstANR engine input to receive an audio input signal, a second ANR engineinput to receive a first supply current from a power supply through afirst electrical path, a third ANR engine input in communication withthe microphone, and an ANR engine output to provide an audio outputsignal; and an acoustic driver amplifier having a first driver amplifierinput to receive a second supply current from the power supply through asecond electrical path, a second driver amplifier input in communicationwith the ANR engine output to receive the audio output signal and adriver amplifier output to provide an amplified audio output signal; acurrent sensor disposed in the second electrical path and having asensor output to provide a signal responsive to a characteristic of thesecond supply current; a signal conditioner module having an input incommunication with the sensor output and having a signal conditioneroutput, the signal conditioner module providing a conditioned signal atthe signal conditioner output in response to the signal responsive tothe characteristic of the second supply current; and an audio and modecontrol module having a first input to receive a source audio signal, asecond input in communication with the signal conditioner output, and anoutput in communication with the first ANR engine input, the audio andmode control module controlling at least one of a mode of operation of aheadphone system and an attribute of the audio input signal in responseto the conditioned signal.
 10. The headphone of claim 9 furthercomprising an acoustic driver having a driver input in communicationwith the driver amplifier output of the acoustic driver amplifier toreceive the amplified audio output signal.
 11. The headphone of claim 9,wherein the attribute of the audio input signal comprises at least oneof a selection of an audio source, a volume, a balance, a mute, a pausefunction, a forward playback function, a playback speed and a reverseplayback function.